dynamic icons with the virtual tree component for delphi

2018-06-12 05:36:14

I need to know how to store and load two different icons for each node in the virtual tree component , also the two icons are different in size

Thanks

Unless you're going to owner-draw the whole thing, no control I'm aware of supports heterogeneous icon sizes, Virtual Treeview include. All icons for a given view are taken from a single TImageList control, and TImageList only supports one image size at a time.

You can make the icons appear to have different sizes by making the image size be that of the larger icon, and then painting the smaller icons onto larger icons that happen to be padded with transparent borders.

If you only need to support one icon size at a time, then you can maintain two separate TImageList controls. When you want to switch sizes, reassign the tree control's ImageList property. You may also need to adjust the DefaultNodeHeight property, along with the heights of all the nodes that already exist.

This works for me using TPngImageList. I assume this implementation should work with standard TImageList, but using png images is a better choice.

In this example the form class name is "TfPrj", the TvirtualStringTree instance name is "vPrj", and TMyDataRecord is the record structure where you get your data.

Your form has a TVirtualStringTree linked to a TPngImageList with 16x16 standard icons set. but you want to use for some nodes a 64x64 icon set.

Create your TPngImageList with 64x64 icon set, called iLarge.

In you code manage a custom drawing like this.

var
  p: TMyDataRecord;

const
  riskImagesSize=64;
  riskImagesPadding=2;

procedure FindP(Node: PVirtualNode);
begin
  // This procedure fill in the "p" record with your tree data for the node.
end;

procedure TfPrj.vPrjMeasureItem(Sender: TBaseVirtualTree; TargetCanvas: TCanvas;
  Node: PVirtualNode; var NodeHeight: Integer);
begin
  FindP(Node);
  if p<>nil then
    if p.LargeImages then
      NodeHeight := riskImagesSize+riskImagesPadding*2;

end;

procedure TfPrj.vPrjBeforeCellPaint(Sender: TBaseVirtualTree;
  TargetCanvas: TCanvas; Node: PVirtualNode; Column: TColumnIndex;
  CellPaintMode: TVTCellPaintMode; CellRect: TRect; var ContentRect: TRect);
begin
  if Column=0 then begin
    FindP(Node);
    if p<>nil then begin
      if p.LargeImages then begin
        Inc(ContentRect.Left,riskImagesSize);
    end;
  end;
end;


procedure TfPrj.vPrjDrawText(Sender: TBaseVirtualTree; TargetCanvas: TCanvas;
  Node: PVirtualNode; Column: TColumnIndex; const Text: string;
  const CellRect: TRect; var DefaultDraw: Boolean);
var
  i: integer;
  s: string;
begin
  FindP(Node);
  if Column=0 then
    if p<>nil then
      if p.LargeImages then begin
        iLarge.Draw(TargetCanvas,CellRect.Left-riskImagesSize-riskImagesPadding*2,CellRect.Top+riskImagesPadding,p.LargeImagesIndex);
      end;
end;

procedure TfPrj.vPrjGetImageIndex(Sender: TBaseVirtualTree; Node: PVirtualNode;
  Kind: TVTImageKind; Column: TColumnIndex; var Ghosted: Boolean;
  var ImageIndex: Integer);
begin
  if Column<>0 then
    Exit;
  FindP(Node);
  if p.LargeImages then
    ImageIndex=-1
  else
    // Assign the image index for standard TPngImageList

end;

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